Insulating air conduit

ABSTRACT

This invention is related to ultra-light conduit for used air and a method for construction of such a conduit with sandwich sheet type of material such as “THERMO-FOIL™” permitting to avoid losses of heat and humid air. The method of construction of a used air rectangular conduit includes the following five (5) steps: 1) cutting of a sandwich sheet 2) sealing around the sandwich sheet 3) heat formation of lengthwise channels on the surface of sandwich sheet 4) assembling the sandwich sheet into a conduit of a predetermined length and 5) installing a lengthwise vertical reinforcement into the conduit and providing a male adaptor to a fore end of the conduit which could be adapted to an aft end of a joining conduit.

FIELD OF INVENTION

This invention belongs to the field of exhausting used air from houses,apartments and commercial buildings and particularly from kitchen hoods,bathroom fans and dryer conduits.

This invention is related to a new method of construction of used airconduits that have a circular or a rectangular cross section and made ofa sandwich of reflective double wall air bubble cushioned material, suchas “THERMO-FOIL™” to prevent losses of heat and humid air.

The method of construction comprises five steps of transformation of asandwich sheet, for a rectangular conduit or for a conduit with acircular section. For a conduit with a rectangular section 1) cutting ofa sandwich sheet, 2) sealing the periphery of the sandwich sheet 3)creating a heat formed channel installed lengthwise to deliminate foursides of a segment 4) assembling the mating ends of a sheet and 5)installing a male adaptor in one end of a segment for joining anotherend of a second segment.

Another method of construction is provided for used air conduits withcircular section by: 1) cutting a sandwich sheet 2) sealing around thesandwich sheet 3) passing through a bender to form a circular section 4)assembling the mating ends of a sheet and 5) putting a male adaptor tojoin another conduit.

PRIOR ART

A review of prior art revealed some patents relating to conduitscomprising insulating material, sheet type or foam type.

The following patents held my attention.

Canadian Patent Application No. 2,049,198, in the name of Lutgen andLaid Open on Aug. 22, 1992, describes an insulator of the sandwich typeconceived to exactly fit the internal shape of cryogenic containers. Thesandwich includes successive layers of thermal insulating materials suchas polystyrene and foams of different densities. To prevent liquid orgas exchanges, sheets must be enclosed in impermeable and rigid wallssuch as the steel walls of a cryogenic reservoir: this increasesconsiderably the construction costs.

Canadian Patent Application No. 2,032,111, in the names of Cur et al.and Laid Open on Jun. 19, 1991, describes an insulator of the sandwichsheet type conceived to be stuck onto a flat face of a refrigerationunit. The sandwich, sealed at its ends, includes superposed lamellaemade of different insulating materials and thin inter-lamellar spacesfilled with air. The insulating sandwich of Cur et Al. is held by a wallof plastic and a wall of metal, this increasing considerablyconstruction costs. Moreover, Cur et Al. do not show joints betweensheets that would indicate how those could form independent structureswithout the existence of plastic and metal walls. Also Cur et Al. do notuse air bubbles as a thermic insulation.

U.S. Pat. No. 5,014,753 Rossignol et Al., May 14, 1991, describes aflexible and impermeable insulator to protect electrical wires againstradiant heating. The insulator comprises a series of successive layersof polymers of which a first layer is of dark particles and a secondclear with particles of metal having a reflecting surface. Rossignol etAl. do not use air bubbles as thermic insulation, nor the principle ofhermetic joint around an empty structure.

U.S. Pat. No. 3,810,491 Hildebrandt, May 14, 1974, describes a method ofmanufacturing insulating conduits of double-walling and circularsection. Conduits of double walling comprise an interior pipe disposedin a coaxial way relatively to an exterior pipe and are insulated in thespace comprised between double-walling. Insulators being constituted ofmany successive layers of insulating materials are separated by airspacing. These are obtained with an insulating method placing insulationin tension rather than compression. The insulating method consists inlaying out insulating bands and spacers in a helicoidal way along thewall of the internal pipe and to remove the spacers to create a tensionbetween the wall of the internal pipe and the wall of the external pipe.This invention requires two conduits with rigid walls. Its use seemsless appropriate for bends or other brutal directional changes or forconduits of rectangular section.

U.S. Pat. No. 3,397,720 Jones, Aug. 20, 1968, reveals an insulationsystem for cryogenic structures made of a sandwich sheet that has manysuccessive layers of insulation material, such as sheets of corrugatedpolyester and other layers of insulation material. Sheets of corrugatedpolyester create space at the center leaving room for air. Thisapplication requires a double-walling pipe to avoid air losses throughinsulating sheets that seem porous. Moreover, this type of corrugatedmaterial, in the construction of sandwich sheets does not make themflexible enough for directional changes such as bends.

Conventional used air conduits made for kitchen hoods are built withgalvanized steel and do not comprise any insulation to prevent heatloss. This type of conduits is available on the market in two L-shapedhalf-conduits to be joined to make a rectangular conduit. The two partsare held together with ends that are not air tight and the conduits donot comprise any adaptor to hold the ends of conduits together,facilitating loss of humid air. This type of conduit does not compriseany thermic insulator, thus favoring humid air condensation in a conduitwhich passes through a cold area of a building or in winter time. So, asthe conduit is not tight to fluid exchanges, humidity and condensingwater may leak into the structure of the building and bring nuisancessuch as moisture or other problems needing repairs or replacement.

None of the inventions mentioned above has a combination of a lightmaterial, not requiring rigid nor expensive walls, but on which thejoints and the perimeter are air-tight, to prevent losses of warm andhumid air.

OBJECTIVES

The first objective of this invention consists in building vapor-tightused air conduits to prevent humid air losses in buildings, a thermicinsulator to avoid humid air condensation within conduits, adaptors andmeans of joining such conduits.

An objective of this invention is to provide a combination comprising abasic material with two external layers of a radiant material, separatedby at least two layers of air bubbles comprised in between five films ofplastic matter (as polyethylene), cut in variable sizes, prefolded indesired shape and assembled by means of adhesive bands and provided withrigid means of coupling at one end of a conduit and at the center of afour foot long straight conduit.

Another object of this invention is to create ventilation conduits thatare light, easy to install and at a lower cost than uninsulated conduitsrequiring the addition of an insulator available in present market.

Another objective is to make four foot long conduits that permit unionwith multiangular bends or internal deflectors.

The last objective is to make used air conduits of rectangular shape (10inches×3¼ inches) for kitchen hoods, used air conduits of circular shapefor bathroom (generally 3 inches) and drying-machine conduits (usually 4inches).

DRAWING FIGURE

I will describe hereinafter more precisely, a method of constructionconsistent with the present invention by referring to annexed drawingsin which:

FIG. 1 is a perspective view of a used air conduct, rectangular, withpartial section.

FIG. 2A is a plan view of the conduit of FIG. 1.

FIG. 2B is a side view of the conduit of FIG. 1.

FIG. 2C is a view from the upstream end of the conduit of FIG. 1.

FIG. 3A is a top view of a conduit, in construction.

FIG. 3B is a section according to line 3B—3B of FIG. 3A.

FIG. 3C is a section according to line 3C—3C of FIG. 3A, in assembly.

FIG. 3D is a close-up view of region 3D of FIG. 3C in closed position.

FIG. 4A is a perspective view with a partial cut of a bend.

FIG. 4B is a perspective view with a partial cut of another bend.

FIG. 5 is a perspective view of a circular conduit with a partialsection.

FIG. 6A is a partial section of a longitudinal junction of a circularconduit in preparation.

FIG. 6B is a partial section of the longitudinal joint of FIG. 6Acompleted.

DESCRIPTION OF THE INVENTION

A preferred embodiment of the subject invention is illustrated in FIG. 1wherein like parts refer to like numbers and which shows:

Air Duct, Rectangular

A rectangular air duct 20 particularly for evacuating used air has aparallelepiped shape and is made of a sandwich sheet 22. The air duct 20comprises a top 24, a bottom 26, a closed side 28 and an opened side 30all forming a rectangular shape, parallel to the major axis 32 and inthe direction of fluid flow. The air duct 20 also comprises openedupstream 34 and downstream 36 ends, it is also of rectangular shape andis parallel to a minor axis 38 and perpendicular to the fluid flow. Thetop 24 is joined to the closed side 28 with an adhesive band 40 on allthe length of the top 24 and of the opened side 30.

A rectangular adaptor 42 comprises two longer sides 44 and two shortersides 46; the rectangular adaptor 42 partly fits into downstream end 36to serve as male end to another air duct on which the upstream end 34serves as the female end.

An elongated C-reinforcement 48 comprises a web 50 and two wings 52.Each wing 52 of the C reinforcement is respectively in contact with thetop 24 and the bottom 26, the web 50 serving as support, theC-reinforcement 48 being near the center of the major axis 32 and of theminor axis 38. The C-reinforcement 48 prevents the collapse of the top24 onto the bottom 26.

FIG. 2A illustrates a view of the top 24 and of the rectangular adaptor42. FIG. 2B is a view of the opened side 30, of the adhesive band 40 andof the rectangular adaptor 42. FIG. 2C illustrates a view of theupstream end 34, the rectangular adaptor 42 and the C-reinforcement 48.

FIGS. 3A, 3B and 3C illustrate different steps of the construction of anair duct 20, 4 foot long, 3¼ foot tall, 10 inch wide. FIG. 3A shows theresult of the first step of construction, namely cutting the sandwichsheet 22 in such a way that it has a rectangular shape with a perimeter54 comprising two sheet long sides 56 of 4 foot in length and two sheetshort sides 58 of 30 inches.

The second step of construction is that of sealing the perimeter 54 ofthe sandwich sheet 22 with a heated angle iron to form a first flat end60 prolonging the opened side 30 and two lateral flat ends 64 prolongingthe sheet short sides 58.

The third step of construction is that of creating V grooves 66 with aheated angle iron to form a first limit 68 between the top 24 and theclosed side 28, a second limit 70 between the closed side 28 et thebottom 26 and a third limit 72 between the bottom and the opened side30.

FIG. 3B illustrates a detail of a side view of the sandwich sheet 22,the first flat end 60, the second flat end 62 and the V grooves 66 afterthe third step. The V grooves 66 have a 45° side 73 to form a isoscelestriangle when the sandwich sheet is on a flat surface.

The sandwich sheet 22 (FIG. 3D) is of THERMO-FOIL™ type and comprises anexternal film 74, an internal film 76, two layers of air cells 78, thefirst flat end 60 (FIG. 3C) prolonging the top 24 and the second flatend 62 prolonging the opened side 30. The air cells 78 act as insulatorswhile the external film 74 and the internal film 76 act like radiantmaterial to keep a gradient of temperature between ambient air and usedair circulating in the air duct. There cannot be any heat loss betweenan environment with ambient air and an environment with used air becausethe first flat end 60 and the second flat end 62 seal a perimeter of thesandwich sheet 22.

FIG. 1 illustrates a wall located longitudinally relatively to a majoraxis parallel to the direction of fluid flow and of which a side isshown on FIG. 3C and presents a rectangular shape comprising a first end88 extending in a first flat end 60 of a long crushed prolonged surface80 of a width of 1½ inch, and a first angular crushing 82 at −45°relatively to the top 24.

A second end 89 extends in a second flat end 62 and comprises a secondangular crushing 86 at 45° relatively to the opened side 30. The secondflat end 62 is crushed on a width of ½ inch and can comprise a smallprolongated surface 84 that overhangs the second angular crushing 86.

FIG. 3C illustrates the fourth step of construction, namely to assemblethe rectangular air duct 20. When the sandwich sheet 22 is folded toform the air duct 20, the first angular crushing 82 and the secondangular crushing 86 join to make a corner of the air duct.

The first flat end 60 located at the first end 88 is to be stuck to theoutside of the opened side 30 and the second flat end 62 located at asecond end 89 is to be stuck on the second crushing end 86 and on thesmall prolongated surface 84 on bottom 24 to form the air duct 20.

FIG. 3D illustrates a detail of the location of the first flat end 60once assembled and held by the adhesive band 40.

The fifth step is that of fitting the rectangular adaptor 42 into thedownstream end 36 and to fix the C-reinforcement 48 (FIG. 1) inside theair duct 20.

FIG. 4A is a perspective view of a vertical bend 90, made for aventilating network with a vertical change in direction.

FIG. 4B is a perspective view of a horizontal bend 92 designed for aventilation network with a horizontal change in direction.

Circular Air Duct

FIG. 5 is a perspective view of a circular air duct 100, that has acylindrical shape and made of a sandwich sheet 22. The circular air duct100 comprises a cylindrical wall 102 having a first end for circle 88′and a second end for circle 89′ which are parallel to a major axis ofcircle 108, an upstream and a downstream ends of circle 110 and 112,opened and with circular sections, and a circular adaptor 114.

The first end for circle 88′ is joined to the second end for circle 89′with an adhesive band for circle 116 on all the length of the circularduct 100.

The circular adaptor 114 is rigid, of cylindrical shape and comprisestwo ends 120; the two ends 120 being opened and comprising a circularsection. The radius of the circular adaptor 114 is shorter than theradius of the circular section by an amount equal to the width of thesandwich sheet 22. The circular adaptor 114 partially fits in the insideof the downstream end of circle 112 to serve as a male to a followingair duct of which the upstream end of circle 110 is used as a female.

To construct the circular duct 100, having a length of 4 feet and adiameter of 3 or 4 inches, there are four steps equivalent to thoseneeded to construct the air duct 20 with rectangular section. A firststep consists in cutting the sheet 22 into a rectangular shape having aperimeter 54 (FIG. 3A) and two sheet long sides 56 of four feet and twosheet short sides 58 of 9½ or 12½ inches.

A second step of construction consists in sealing the perimeter 54 ofthe sandwich sheet 22 with a heated angle iron to form a first flat endfor circle 122 (FIG. 6A) prolonging the first end for circle 88′, asecond flat end for circle 124 prolonging the second end for circle 89′and two lateral flat ends for circle 126 prolonging the sheet shortsides 58.

FIG. 6A shows a detail of the first end for circle 88′ that comprises afirst flat end 122 that comprises a ½ inch wide prolongated externalcrushing and an angular side 130 angular relatively to the cylindricalwall 102.

The second side 124 prolongs itself towards the interior, over a widthof ½ inch, and has a 135° side 134.

A third step of construction is that of assembling the circular duct100. The first flat end 122 is to be stuck outside of the second end 89and the second flat end 124 is to be stuck under the first end 88 toform a continuous circular duct 100.

FIG. 6B illustrates the location of the first and second flat ends 122and 124 with external and internal prolongations once assembled andenforced with an adhesive band 116.

A fourth step of construction is to put the sheet for the circular duct100 through a bender to get a perfectly cylindrical product. This stepis optional.

A fifth step of construction is that of fitting the circular adaptor 114into the downstream end 112.

I have discovered that the condensation problem caused by heat loss inused air conduit is resolved by using a sandwich sheet such asTHERMO-FOIL™ with thermic insulation properties superior to those offoams or sandwiches made of lamellae of different insulating materials.I have also discovered that the problem of humid air loss caused by usedair conduits that are not air-tight is resolved by sealing the perimeterat each joint by material of the sandwich sheet and in using an adaptorlocated judiciously in a used air system.

The reflective sandwich sheet material is made of a sandwich comprisingtwo layers of air cells and serving as thermic insulator and on which issuperinposed on top and bottom a sheet of impermeable and radiantmaterial.

So the sandwich sheet may successively comprise an aluminum sheet, twolayers of air bubbles contained within three films of a plastic sheetcoated with a material that might be fireproof, and another aluminumsheet; or comprise an external aluminum sheet, a layer of air cells andan internal polyethylene sheet; or it might also be constructed with anexternal polyethylene sheet, a layer of air cells and an internalpolyethylene sheet.

SUMMARY OF INVENTION

A general objective is to create an air duct comprising a number ofsegments, each one longitudinally oriented relatively to a major axis 32parallel to the direction of used air flow and comprising a walldelimiting an interior space which permits air flow, the wall being ofuniform thickness and made of a rectangular sandwich sheet comprisingair cells confined between a first external film and a second internalfilm, the second internal film coinciding with the wrapping of theinternal space, each segment comprising an opened downstream end 36 andan upstream end 34, and means for coupling fitted into the downstreamend 36 to become the male end when joined with another segment, or tocouple an used air conduit to a female end of another type of conduit,the upstream end being the female end receiving the above male end.

The sheet may comprise: a first end 88 coinciding with the length of therectangular sheet to form the longitudinal joint of the segment with acorresponding second end 89, the first end terminating by a first 45°angular crushing 82 extended in a first flat end 60 and a second end 89ending with a second angular 45° crushing 86 extended into a second flatend 62 that folds up onto the second angular 45° crushing 86, the first45° angular crushing 82 leaning on the second flat end 62, the firstflat end edge 60 settling onto the second end along the first externalfilm. The wall comprises means of adhesion to seal and hold together thefirst and second ends.

The coupling means comprise an adaptor 42 with an external face 43adjacent to the second internal film 76 of the wall, partly extendedoutside of the downstream end 36 of the segment and that can be sled inthe upstream end of an adjacent segment or series of segments. The wallalso comprises lateral flat ends to seal sandwich material at upstreamand downstream ends.

The wall may also form a parallelepiped that has a rectangular sectioncomprising a top 24 extended in the first flat end 60, a closed side 28,a bottom 26, an opened side 30 extended by the second flat end 62 and atleast three longitudinal folding lines of which one demarcating a firstlimit 68, between the top 24 and the closed side 28, another demarcatinga second limit 70 between the closed side 28 and the bottom and a thirdone demarcating a third limit, between the bottom and the opened side,the parallelepiped comprising means of reinforcement orientated alongthe major axis, in contact with top and bottom, to prevent collapsing ofthe top onto the bottom.

The rigid adaptor may be of parallelepiped shape and comprises twoopened ends and a rectangular piece of length l and width w bothinferior by twice the thickness t of the wall, relative to the length Land width W of the rectangular section of the segment, according to theequations L=2t+l and W=2t+w. The adaptor will lean against the internalside of an opening delimited by the top, the closed side, the bottom andthe opened side of the segment.

Means of reinforcement is a C shaped reinforcement comprising a web andtwo wings, each one respectfully touching top and bottom. The wings ofthe C are placed parallel to the major axis and the web serves assupport.

The first flat end is joined to the end of the opened side by means ofadhesion located on the entire length of the opened side. Means ofadhesion of the air duct is an aluminum band of the Mactac™ type locatedover the entire length of the wall, to join the first flat end to thesecond one.

The wall may be cylindrical, in which case it comprises a first andsecond ends, the upstream and downstream ends being a circular sectionof radius R, means of coupling being a rigid adaptor comprising acylindrical wall and two opened ends of radius r inferior by the amountof the thickness of the cylindrical wall, relatively to the radius ofupstream and downstream ends, namely R=r+t.

Method of Construction

The air duct may be made with rigid insulation material and involves thefollowing steps:

a step of cutting the sandwich of insulating material delimiting aperimeter of predetermined size.

a step of sealing the perimeter to prevent fluid exchanges, gaseous orliquid, between the interior of the insulating material and thesurroundings, the sealing step comprising a step of crushing the firstand the second ends,

a step of folding the sandwich around the major axis according to adesired shape,

a step of assembling of the first and second flat ends by means ofadhesives to complete the shape of the section,

a step of installing of a rigid adaptor fitted into the downstream end.

If the air duct is of parallelepiped form with a rectangular sectioncomprising a top, a bottom, a closed and an opened sides, the methodcomprises these additional steps of construction:

a step of folding by heating means the sandwich to obtain the angles,top, bottom, closed and opened sides required to have a rectangular airduct,

a step of preparation of a C-reinforcement in making a web and two wingswith the insulating material,

a step of installation of the C wings respectively in contact with topand bottom, the web serving as reinforcement.

The sandwich may be a sheet comprising many layers of material, foursides and a perimeter. The sealing steps of the perimeter consists inheating the perimeter with an angled-iron in such a way that the layersof the sandwich that form the insulation material melt to make four thinbands on each of the four sides of the sheet, of which two arerespectively part of the first flat end of top and the second flat endof the opened side, the first flat end when installed, should be infront of the second flat end of the folded sheet.

The width of the first flat end of the top is bigger than the width ofthe second flat end of the opened side so as to reinforce any jointbetween the top and the opened side, the first flat end of the top isinstalled, against the outside face of the opened side, the second flatend of the opened side being placed under the bottom face of the topside.

The step of folding the sandwich consists in heating the sandwich withan angle iron so it will produce three V grooves within the wall of thesandwich. The V grooves having 135° sides form an isosceles trianglewhen the sandwich is flat on the ground: the V grooves respectivelydefine a first limit between top and closed side, a second limit betweenclosed side and bottom and a third one between bottom and opened side.When the sandwich is folded to built the rectangular air duct, the 135°sides are connecting, to create angles forming the rectangular air duct.

A further assembling step consists in sticking the first flat end of thetop against the outside of the opened side, with an adhesive band on allthe length of the first flat end. Means of adhesives may be analuminized adhesive band of the Mactac™ type installed on the fulllength of a joint, between the first and second flat end.

The sealing step of the perimeter of the insulating material consists inheating the perimeter with a hot angle iron in such a way that thelayers of the sandwich that form the insulation material melt to createa thin band and a 135° side, the first flat end with the 135° side 134being set inside the cylindrical wall, the second flat end with the 135°angled side being set outside the cylindrical wall.

The folding step requires an additional step of circulating the air ductwith the assistance of a roll folding device. The second flat end 124leans against the interior of the cylindrical wall to obtain acontinuous cylindrical wall.

The installation step comprises the jointing of a circular adaptorinside a downstream end, the adaptor being rigid and comprising acylindrical wall and two ends.

It is clear that the method of realization of the present inventionbeing described above, referring to annexed figures is provided as anindication and not limiting. Modifications and adaptations may be madewithout parting with the objectives of the present invention.

Other embodiments of the above invention are also possible and notlimited to the scope of the following Claims.

PARTS LIST

20 air duct

22 sheet

24 top

26 bottom

28 closed side

30 opened side

32 major axis

34 upstream end

36 downstream end

38 minor axis

40 adhesive band

42 rectangular adaptor

43 external face

44 longer side

46 shorter side

48 C reinforcement

50 web

52 wing

54 perimeter

56 sheet long side

58 sheet short side

60 first flat end

62 second flat end

64 lateral flat end

66 V groove

68 first limit

70 second limit

72 third limit

73 45° side

74 external film

76 internal film

78 air cell

80 long prolonged surface

82 first angular crushing

84 small prolonged surface

86 second angular 45° crushing

88 first end for rectangle

88 ¹ first end for rectangle

89 second end for rectangle

89 ¹ second end for circle

90 vertical bend

92 horizontal bend

100 circular duct

102 cylindrical wall

108 major axis of circle

110 upstream end of circle

112 downstream end of circle

114 circular adaptor

116 adhesive band for circle

120 ends

122 first flat end for circle

124 second flat end for circle

126 lateral flat end for circle

130 angled side

134 135° side

What is claimed is:
 1. An air duct comprising: one or more segments,each segment disposed longitudinally relatively to a major axis parallelto an air flow, each segment comprising a wall defining an internalspace that permits flow of said air, said wall being uniformly thick andmade of a sandwich material comprising air cells contained between afirst external film and a second internal film, said second internalfilm coinciding with the internal space, each said segment comprising anupstream end and a downstream end, said upstream end and said downstreamend being opened, each segment comprising means for coupling fitted atone of said ends to join a segment to another segments, wherein saidwall forms a parallelepiped with a rectangular section comprising a top,a closed side, a bottom, an opened side, and at least three longitudinallines for folding of which one demarcating a first limit, between saidtop and said closed side, another demarcating a second limit betweensaid closed side and said bottom, and a third demarcating a third limit,between said bottom and said opened side, said parallelepiped comprisingmeans for reinforcement orientated along said major axis, touching saidtop and bottom.
 2. An air duct as defined in claim 1, wherein said wallcomprises: a first end longitudinal relatively to said segment and asecond end also longitudinal, said first end ending with a first angularcrushing, extended in a first flat end, said second end ending with asecond angular crushing extended in a second flat end to be folded onsaid second angular crushing, said first angular crushing leaningagainst said second flat end, said first end setting itself beyond saidsecond end, along said first external film, said wall also comprisingmeans for adhesion to make said conduit airtight and to hold togethersaid first end and said second end.
 3. An air duct as defined in claim2, wherein said top is prolonged by said first flat end an said openedside is prolonged by said second flat end.
 4. An air duct as defined inclaim 3, wherein said first flat end is joined to said end of saidopened side by means for adhesion placed on all length of said openedside.
 5. An air duct as defined in claim 4, wherein means for adhesionis an aluminized adhesive band, located on all length of said wall andjoining said first flat end to said second end.
 6. An air duct asdefined in claim 1, wherein said means for coupling comprise an adapterwith an external face adjacent to said second internal film of saidwall, said adapter partly extended outside of said downstream end forinserting into said upstream end of an adjacent segment, said wallcomprising lateral crushed ends to seal said sandwich material at saidupstream and downstream ends.
 7. An air duct as defined in claim 1,wherein said means for coupling is a parallelepiped rigid adaptercomprising two opened sides and a rectangular section adapted to leanonto an internal side of an aperture defined by said top, closed side,bottom and opened side.
 8. An air duct as defined in claim 1, whereinsaid means for reinforcement is a C-reinforcement comprising a web andtwo wings wherein each of said wings is respectively in contact withsaid top and said bottom, said web serving as reinforcement, to avoidcollapsing of said top onto said bottom.